Synergistic mixture of pour depressants for middle distillates



- Acryloid and their modifications.

United States Patent Ofifice The present invention is concerned withimproving the flow of fuels at low temperatures and improving pour pointcharacteristics of middle distillates. More particularly, the inventionrelates to the preparation of improvedlow cold test hydrocarbon fuels,in particular heating oils and diesel fuels, kerosene, aviationturbo-jet fuels, and other fuels that are subject to low temperatures.The preferred class of pour depressants of the present invention aresynergistic mixtures of pour depressants, which mixtures comprise incombination an acylatcd polystyrene used in conjunction with a pourdepressant selected from the class consisting of an alkylatedpolystyrene and copolymer of ethylene and vinyl acetate.

With the increase in the use of hydrocarbon fuels of all kinds, aserious problem has arisen in areas frequently subject to lowtemperatures in the cold test characteristics of fuels. Particularly,serious problems have been encountered by heating oils and diesel andjet fuels that have too high a pour point, resulting either indistributional or operating difiiculties or both. For example, thedistribution of heating oils by pumping or syphoning is rendereddifiicult or impossible at temperatures around or below the pour pointof the oil. Furthermore, the flow of the oil at such temperaturesthrough the filters cannot be maintained, leading to the failure of theequipment to operate.

It is, of course, well known to add pour depressants to lubricating oilsto lower the pour point. These lube oil additives, mostly high molecularweight organic compositions formed by alkylation of benzene ornaphthalene or derivatives thereof or by polymerization of lowermolecular weight methacrylates, or by condensation polymerization ofvarious kinds, are not satisfactory in service with middle distillateand lighter fuels. Poor performance of these additives might possiblyresult from the structural differences between waxes occurring inlubricating oils and so-called middle distillates.

A wide variety of compounds have been found to be effective as pourpoint depressants for lubricating oil. Among the best known areParaflow, Santopour, and They are prepared either by condensing aromaticcompounds with long chain paraffins, such as wax, or by condensingolefinic esters.

It is generally considered that these pour depressants.

are effective in that in cooling an additive-containing oil, thehydrocarbon chain of the additive becomes incorporated into the crystallattice of the separated wax, while the other part of the pourdepressant molecule prevents the crystals from adhering together to forma gel structure. The failure of these additives to be elfective inmiddle distillates may at least in part be due to the basic differencein the composition between the wax in lubricating oils'and that inmiddle distillate fuels.

It is, therefore, the principal object of the present invention to setforth an improved pour depressant for middle distillate and lighterfuels. The boiling ranges of these oils are generally about 250 to 750F.

The petroleum distillate fuels in which the additive materials or" theinvention are employed consist of a major proportion, at least 95 ofliquid hydrocarbons boiling at temperatures between about 70 F. andabout 750 F. These fuels include gasolines such as aviation,

3,069,245 Patented Dec. 18, 1962 marine and automotive or motorgasolines, aviation turbojet fuels such as JP-l, P4 and JP-5 fuels, anddiesel fuels such as marine, stationary and automotive diesel enginefuels.

Aviation turbo-jet fuel consists of at least of a mixture of volatilehydrocarbons. It is defined by U.S. Military Specifications MILF5616 andMIL-F-5624C. Its volatility is such that its end point does not exceed572 F. Its. viscosity is between 0.5 and 1.5 centistokes at F.

Diesel fuels as referred to in connection with the invention consist ofat least 95% of a mixture of hydrocarbons boiling between 250 F. and 750F. either by ASTM Method D8656 when their end points do not exceed 600F. or by ASTM Method D-158-54. Diesel fuels are defined by ASTMSpecification D-97553T and fall into grades 1D, 2D and 4D, in all ofwhich the additive materials of the invention may be used. They haveviscosities betwen 1.4 and 26.4 centistokes.

The liquid fuels in which the additive materials may be incorporatedthus comprise at least 95% by weight of a mixture of hydrocarbons havinga boiling range between the limits of 75 F. and 750 F. and a viscositybetween the limits of 0.264 and 26.4 centistokes at 100 F.

In accordance with the present invention, a synergistic mixture is usedwhich comprises an acylatcd polystyrene used in conjunction with amaterial selected from the class consisting of an alkylated polystyreneand a copolymer of ethylene and vinyl acetate.

The acylatcd polystyrene of the present invention used in conjunctionwith the alkylated polystyrene or the copolymer of ethylene and vinylacetate are prepared with said fatty acid chlorides of criticalcomposition and themselves are active pour depressants for middledistillatesQ The acylates of interest have the following structure:

where the acyl group is defined according to the contributory numbertable and R is normally a straight chain alkyl group of about C to C andx is a number from 3 to 20.

In general, the method of acylation may vary appreciably. The methodswhich are disclosed in U.S. Patent No. 2,703,817 entitled Process forthe Preparation of Lubricating Oil Additives, inventor: George E.Serniuk, and in U.S. Patent No. 2,500,082 entitled "Acylated Derivativesof High Molecular Weight Copolymers, inventors: Eugene Lieber andWilliam H. Smyers, may .be utilized.

Broadly, the method of acylation comprises dissolving the polystyrene ina suitable solvent, such as chlorobenzene, o-dichlorobenzene, or tetrachloro-ethylene andadding to the solution the equimolar carboxylic acidchloride/ aluminum chloride complex at temperatures of 30 to 70 C.(preferably 40 to 60 C.), with provision for carrying away the evolvedhydrogen chloride. After all the acid chloride/aluminum chloride complexhas been added (one mole per mole of phenyl groups in the polystyrene,plus a slight excess) and hydrogen chloride evolualcohol, the acylate istaken up in a suitable solvent, such as heptane or kerosene and washedwith water and alkaline solutions. The resinous product may be isolatedas the pure material by evaporating all solvents, or it may be used insolution for making blends in middle distillates.

For obtaining the superior pour point depressants of this invention, itis desired that the polystyrene starting material have an intrinsicviscosity within a range of about 0.2 to 2.0, preferably 0.8 to 1.5.These viscosities correspond to molecular weights within a range of fromabout 10,000 to 75,000, preferably 30,000 to 60,000 Staudinger (if theconstant for isobutylene polymers is assumed to apply). Since theamounts of the other reactants are based on the weight of thepolystyrene, the amount of polystyrene used will depend uponrestrictions such as equipment capacity, etc. The cryoscopic molecularweight after acylation was about 700 to 5,000; the intrinsic viscosityabout 0.1 to 0.5. The 700 molecular weight comprises, in essence, atrimer containing three acylated phenyl groups, whereas, the 5,000molecular weight comprises, in essence, about 18 acylated phenyl groups,on the average, per polymer molecule.

The acylating agent chosen for the preparation of the improved pourpoint depressants of this invention will be aliphatic in nature and willpreferably contain from 8 to 16 carbon atoms in a straight chain.Although C C C C and C acid chlorides are used in the examplesspecifically detailing the instant invention, any straight chain acidchlorides having the above requirements may be used. It is preferredthat equimolar quantities of polystyrene and the acylating agent beused; however, from 0.80 to 1.20 mols of acylating agent per molequivalent of polystyrene is operable. A large excess of acylatingagents does no harm, but it does not react and so is wasted.

The acylated polystyrene as described above is used in conjunction witheither an alkylated polystyrene or with a copolymer of ethylene andvinyl acetate. The alkylated polystyrene compounds are prepared withcertain olefins and have a critical composition. The olefin should havea molecular weight in the range 200 to 250 and if it is a mixture atleast 95 mole percent of the olefins should have molecular weightsindividually in the range of 170 to 280. The alkylates of interest ithave the following structure:

H (-CHOH2) XH R is an alkyl group, straight or branched, containing 9carbon atoms or less while R is a straight-chain alkyl group containing10 carbon atoms or more, x is the num- '7:

ber from 3 to inclusive and y is 0.75 .to 2.00.

All products were made under the reaction conditions of solvent,temperature, catalyst and finishing procedure as described in U.S.Patent No. 2,756,265 assigned to Esso Research and Engineering Company,entitled Alkylated Polystyrene Pour Depressants, inventor: William C.Hollyday, Jr.

Broadly, the process comprises the steps of dissolving the desiredpolystyrene in an inert solvent and heating the mixture until thepolystyrene is completely in solution. The mixture is then cooled to thedesired reaction temperature at which time the nitrobenzene and theFriedel-Crafts catalyst is added. The alkylating agent is then addeddropwise and the reaction temperature selected is maintained by coolingor heating as necessary. After the completion of the reaction, thealkylates are purified by well known techniques, among which isprecipitation with methanol, dissolving in hexane and reprecipitatingseveral times With methanol or isopropanol. If desired, the alkylatedmaterial may be dissolved in oil, washed with alkaline solutions, andthe oil solution then steam stripped to result in the final product.

For obtaining the superior pour point depressants of this invention, itis desired that the polystyrene starting material have an intrinsicviscosity within a range of about 0.2 to 1.0, preferably 0.8 to 1.5.These viscosities correspond to molecular weights within a range fromabout 10,000 to 75,000, preferably 30,000 to 60,000 Staudinger. Sincethe amounts of the other reactants are based on the weight of thepolystyrene, the amount of polystyrene used will depend uponrestrictions such as equipment capacity, etc. The cryoscopic molecularweight after alkylation was about 700 to 3,000; the intrinsic viscosityabout 0.1 to 0.5 The 700 molecular weight comprises, in essence, atrimer containing three alkylated phenyl groups, whereas the 3,000molecular weight comprises, in essence, about eight alkylated phenylgroups.

The alkylation agent chosen for the preparation of the improved pourpoint depressants of this invention will be olefinic in nature and willpreferably contain from 12 to 18 carbon atoms in a straight chain.Although dodecene-l through eicosylene and cracked wax are used, anyolefinic material having the above requirements may be used. It ispreferred that equimolar quantities of polystyrene and the alkylatingagent be used, however, from 0.80 to 2.00 mols of alkylation agent permol equivalent of polystyrene is operable.

These alkylated polystyrenes should be prepared wherein the olefinmixture has a molecular weight of about 224 (that of n-hexadecene). Thepolystyrenes should have a molecular weight within a range of from about10,000 to 75,000, preferably 30 to 60,000 Staudinger. These molecularweights correspond to intrinsic viscosities within the range of from 0.2to 2.0, preferably 0.8 to 1.0. The alkylating agent contemplatedcontains 12 to 20 carbon atoms in a straight chain. A chlorinatedaromatic hydrocarbon is used as a solvent and a Friedel- Crafts catalystin amounts varying between about 10 and 20% by weight based on theweight of the polystyrene. The preferred catalyst modifier,nitrobenzene, is present in amounts so that the mol ratio ofnitrobenzene to the catalyst is from 0.2 to 0.8. Reaction temperatureswithin a range of from to F. are used. These operable reactionconditions are so adjusted that in the relationship K varies between 6.0and 15, where C equals the weight ratio of catalyst to polystyrene, T isthe temperature F., and R is the ratio of mols of catalyst modifier tomols of aluminum chloride. By this particular process advantageousyields of an alkylated polystyrene pour depressant having an overallactivity in a wide range of lubricating oils may be obtained.

As pointed out heretofore, the pour depressant agents have a cryoscopicmolecular weight in the range from about 700 to 3,000 and an intrinsicviscosity in the range from about 0.1 to 0.5. These compounds are usedin a weight concentration of about 0.002 to 0.20. A somewhat morepreferred concentration is in the range from about 0.005 to 0.5 weightpercent. A very desirable concentration to be used is in the range fromabout 0.01 to 0.3 weight percent.

The second class of pour depressants to be used in conjunction with theacylated polystyrene as described above are copolymers of ethylene and avinyl acetate. It is preferred that the parts by weight of ethylene inthe eopolymer be in the range from about 60 to 99% as compared to partsby weight of vinyl acetate in the range from about 40 to about 1%. Avery desirable ethylenevinyl acetate copolymer contains from about 15 to25% by weight of vinyl acetate, as for example about 20% parts by weightof vinyl acetate.

The molecular Weights of the ethylene-vinyl acetate copolymer arecritical and should be in the range from about 1,000 to 3,000,preferably in the range from about 1,500 to 2,200. The molecular weightsare determined by K. Rasts method (Ber. 55, 1051, 3727 (1922)).

The ethylene-vinyl acetate copolymer as described above is used usuallyin a concentration in the range from about .001 to .5 by weight,preferably in a concentration in the range from about .005 to .1% byweight. The low molecular weight copolymers may be prepared by anyperoxide process. In some instances, it may be desirable to firstprepare a higher average molecular weight polymerization product andthen recover from that product material having a molecular weight withinthe range between about 1,000 and about 3,000. Since such polymerizationproducts normally consist of a smear of polymers whose molecular weightsvary over a wide range, an effective method for recovering the 1,000 to3.000 molecular weight portion therefrom is to extract the prdouct witha solvent such as normal heptane or methyl-ethyl ketone. Other methodsfor obtaining the low molecular weight materials include thermaldegradation of the high molecular weight polymer or treatment of thehigh molecular weight polymer with ozone in order to break the polymerchains. Still other methods also useful will be apparent to thoseskilled in the art.

A very desirable method is to conduct polymerization in a benzenesolution using di-tertiary-butyl-peroxide' as an initiator at atemperature in the range from about 280 to 340 F. The preferredtemperature is about 300 'F. The pressure is in the range from about7-00 to 2,000 pounds, preferably at about 800 pounds. The autoclave orsimilar equipment containing the solvent, initiator and vinyl acetate ispurged about three times with nitrogen, twice with ethylene and thencharged with a sulficient amount of ethylene to yield the desiredpressure when heated to the reaction temperature. During thepolymerization, additional ethylene is added whenever the pressure dropsby about 100 p.s.i.g. Polymerization is considered complete when it isless than 50 p.s.i.g. pressure drop per hour. The product is strippedfree of solid and unreacted vinyl acetate under vacuum.

Various amounts of the pour depressants and the various salts wereutilized in distillate fuels. A typical distillate fuel boiling in therange from 250 to 750 F. to which the present additives may be added aremiddle distillate heating oils. These fuels are of commercial grade andhave typical properties as follows:

The improvements obtained by adding the additives in accordance with thepresent invention are set forth in the following table. All pour pointsquoted hereafter were obtained by ASTM Method D-97-47.

The total amount of the pour depressant utilized is preferably in therange from about 0.001 to 0.500 weight percent based upon the amount ofbase stock. It is preferred that a total amount of pour depressant be inthe range from about 0.002 to 0.100 weight percent. The relative amountsof the acylated polystyrene as compared to the alkylated polystyrene orthe copolymer of ethylene and vinyl acetate may vary broadly as forexample from 10 to 90 weight percent of the acylated polystyrene to to10 percent of either the alkylated polystyrene or the copolymer.However, it is preferred that the range be from about 25 to 75 weightpercentof the acylated polystyrene as compared to 75 to 25 weightpercent of either the alkylated polystyrene or the copolymer.

The synergistic efiects secured by the particular mixture of compoundshereinafter described are illustrated by the data in the following TableI. It will be noted that replacement of half the more active pourdepressant with the less active pour depressant does not give theexpected reduction in activity. Instead, the mixture is usuallymore-active than an equal concentration of either component. This canresult in appreciable savings of polymer required to reach a given pourpoint, with a consequent reduction in cost.

TABLE I Synergistic Combinations of Pour Depressants Pour Point, F.,With Total Additive Indicated w Base stock description percent Doly- (A)Acyl 50/50 (B) mer polystymixture Cornrene I (A)+(B) ponent I. (B)Component is Alkyl Polystyrene Straight Run Heating 5 -5 Oil fromCanadian" y 11 Vinyl Acetate Copolymer Straight Run Heating 0.01 -5 5Oil from Venezuela 0.02 15 20 -l0 Crude, +l0 F 0.03 20 30 20 OriginalPour Point 5 0.05 -25 35 25 Straight Run Heatin 0.01 0 5 +5 011 f1 omOanadrarn. 0.05 20 25 -15 Crude, +l5 F 0. 10 30 35 25 Original PourPoint 4 1 Product prepared by acylating polystyrene with 0.25 moledecanoyl chloride, 0.50 mole dodecanoyl chloride and 0.25 moletetradecanoyl chloride per mole of phenyl groups. Intrinsic viscosity0.055.

2 Product prepared by alkylating polystyrene with 0.09 mole C 0.18 moleC14, 0.40 mole Om, 0.27 mole C13, and 0.06 mole C20 11-0lefins per moleof phenyl groups. Intrinsic viscosity 0.122, cryoscopic molecular weight925.

3 Product contains 84 wt. percent ethylene and 16 wt. percent vinylacetate. Intrinsic viscosity 0.124, cryoscopic molecular weight 1150.

4 Boiling range 3l6685 F., 39.0 API gravity, 3.25 cs. at F. viscosity 5Boiling range 35 1-624 F., 37 .4 API gravity, 2.35 cs. at 100 F.viscosity What is claimed is:

1. A petroleum distillate fuel composition having an improved pour whichcomprises essentially a petroleum distillate fuel boiling in the rangefrom about 250 F. and about 750 P. which has been improved with respectto pour point by the incorporation therein of a pour depressingeflective amount in the range from about .001% to .05% by weight of ablend consisting essentially of about 10% to 90% by weight of anacylated polystyrene having a structural formula as follows:

wherein R is a straight chain alkyl group of about 7 to 15 carbon atomsand x is a number from 3 to 20 and 90% to 10% by weight of a compoundselected from the class consisting of an alkylated polystyrene andcopolymer of ethylene and vinyl acetate, said copolymer beingcharacterized by having a molecular weight in the range from about 1000to 3000 and being further characterized by containing from about 1% to40% by weight of vinyl acetate in the copolymer, said alkylatedpolystyrene being characterized by having a molecular 10 weight in therange from about 700 to about 3000 and being further characterized byhaving one alkyl group containing from about 14 to about 18 carbon atomsper ring.

2. The fuel composition of claim 1 wherein said blend consistsessentially of 40 to 60% by weight of said acylated polystyrene and 60to 40% by weight of a compound selected from the class consisting of analkylated polystyrene, and a copolyrner of ethylene and vinyl acetate.

3. The fuel composition of claim 1 wherein the molecular weight of thecopolymer of ethylene and vinyl acetate is in the range from about 1500to 2200.

Coffman et a1. Mar. 7, 1950 Serniuk Mar. 8, l955

1.A PETROLEUM DISTILLATE FUEL COMPOSITION HAVING AN IMPROVED POUR WHICH COMPRISSES ESSENTIALLY A PETROLEUM DISTILLATE FUEL BOILING IN THE RANGE FROM ABOUT 250*F. AND ABOUT 750*F. WHICH HAS BEEN IMPROVED WITH RESPECT TO POUR POINT BY THE INCORPORATION THEREIN OF A POUR DEPRESSING EFFECTIVE AMOUNT IN THE RANGE FROM ABOUT .001% TO .05% BY WEIGHT OF A BLEND CONSISTING ESSENTIALLY OF ABOUT 10% TO 90% BY WEIGHT OF AN ACYLATED POLYSTYRENE HAVING A STRUCTURAL FORMULA AS FOLLOWS: 